<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>let用途</title>
</head>
<body>

<script src="traceur.js"></script>
<script src="bootstrap.js"></script>
<script>
    var a=100;
    let b=200;
    console.log(a);//100
    console.log(b);//200
</script>
</body>
</html>